Trangenic animal mutation models provide new approaches to studies of in vivo mutagenesis and carcinogenesis. The overall goal of this research is to develop and characterize transgenic fish models that can address the dual needs for improved methods to assess genetic health risks associated with exposure to chemical and physical mutagens, and for non-mammalian models for comparative mechanistic studies of in vivo mutagenesis. The proposed studies build on research progress to develop a transgenic model using medaka (Oryzias latipes) that carry a bacteriophage lambda vector harboring lacl and cll as mutation target genes. Following exposure of fish to a mutagen, the target genes are recovered from various tissues using in vitro packaging and transferred into indicator bacteria to quantify mutations. Advantages of using this assay for in vivo mutagenesis are combined with the numerous benefits afforded by fish as animal models including sensitivity, amenability to a wide range of exposure conditions, and low cost. Aim 1 is directed at characterizing mutational responses of transgenic fish exposed to mutagens at early life stages. Objectives are to define whether embryonic or juvenile fish exhibit high sensitivity to genotoxins similar to that observed using other toxicological endpoints, and to determine if mutational responses change at critical stages. An expected outcome will be an improved approach to study of mutations in genes affecting embryogenesis and development. Aim 2 is to characterize unique capabilities of transgenic fish as new novel models for studies of UV- mutagenesis, ocular mutagenesis, and antimutagenesis. Specific toxicity evaluations will study mutations in the skin following UV-B irradiation, mutagenicity of methylazooxymethanol acetate (MAMAc) shown to induce retinoblastomas, and test the inhibitory effects of green tea on mutations caused by dimethylnitrosamine and benzo[a]pyrene exposure. The third aim is to characterize new transgenic medaka and mummichog (Fundulus heteroclitus) lineages carrying the plasmid pUR288 vector containing lacZ as the mutational target. Objectives are to test whether the lacZ target is a reliable marker of induced mutations, particularly for detecting mutations induced by clastogenic agents supporting these fish as models for in vivo mutagenesis. The common goal of the three aims is to characterize mutagenic responses of transgenic fish models sufficient to justify their application in comparative mutagenesis studies and ensure their optimal utilization by the biomedical and environmental health research communities.